1. Field of the Invention
The present invention relates generally to a system and method for operating a motor vehicle. More particularly, the invention relates to a method for inferring the operational status of a vehicle starter motor.
2. Background Art
Early disengagement of a vehicle starter motor can result in no-start, reverse run and air/fuel mixture conditions that can damage or diminish the longevity of engine components. These problems often arise, for example, when an operator attempts to crank a vehicle""s starter but prematurely releases the vehicle ignition switch. If the switch is not held in the START position for a long enough period of time, a spring mechanism inside the switch will push the key back to the switch""s RUN position, thus disconnecting the battery from the starter solenoid and disengaging the starter motor. Repeated misstarts may degrade the starter motor and reduce its longevity, increase vehicle fuel emissions during vehicle cold start conditions, and also affect a customer""s satisfaction with the vehicle.
As such, in order to prevent reverse run and other conditions that may result in inappropriate ignition of an air/fuel mixture, it is desirable when starting the vehicle to know whether the starter motor is engaged or disengaged. By knowing whether the starter is disengaged, for example, a vehicle""s control system can be operated to cease fuel supply and/or deactivate spark actuation so as to avoid a reverse rotation xe2x80x9cbackfirexe2x80x9d condition of the engine. Knowledge of the starter operational state can also be used in scheduling power-up of other vehicle electrical subsystems or components, for example climate control, entertainment and navigational subsystems. Conventional systems for monitoring starter operation however utilize rotation detectors that typically do not differentiate between forward and reverse rotary motion of the engine. Other alternatives, such as key and rotary position sensors, are costly and more difficult to implement into a typical vehicle control strategy.
Accordingly, the inventors herein have recognized an opportunity for inferring the operational state of a vehicle starter motor by monitoring changes in battery voltage during the vehicle starting process.
The aforedescribed limitations of conventional automobile starting systems are substantially overcome by the present invention, in which a method is provided for determining an operational state of a vehicle starter motor coupled to vehicle battery. The method includes the steps of detecting a vehicle battery voltage, deriving an average (xe2x80x9cfilteredxe2x80x9d or xe2x80x9csteady-statexe2x80x9d) vehicle battery voltage and inferring the operational state of the starter motor based at least in part on a difference between the detected vehicle battery voltage and the filtered vehicle battery voltage.
An advantage of the present invention is that the operational state of a vehicle starter motor can be accurately determined without using an engine rotation detector or starter voltage/current sensor hard-wired to a vehicle""s engine or powertrain controller. In accordance with the present invention, the engagement and disengagement of the starter may be inferred from changes in the battery voltage without wiring and control module costs associated with hard-wired sensors. The disclosed method and system can be used advantageously to minimize occurrences of vehicle no-starts, avoid reverse rotation of the engine and prevent undesired ignition of an air/fuel mixture.
Further advantages, objects and features of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.